Variable resistor



O 1959 R HOLLINGSWORTH 2,907,970

VARIABLE RESISTOR Filed Nov. 4, 1957 INVENTOR A. [[f HOZU/V6SI I ORT 7:

ATTORNEYS United States Patent ce VARIABLE RESISTOR R Lee Hollingsworth, West Hempstead, N.Y.

Application November 4, 1957, Serial No. 694,409

6 Claims. (Cl. 338-151) The present invention is related to electrical current modifying devices and is more particularly concerned with an improvement in devices for inclusion in electrical circuits as a variable resistor.

The principal object of my invention is to provide an operable rotary type electrical control which requires a minimum of effort to operate and comprises elements which can be quickly and easily assembled.

My invention is described as follows:

In the drawings:

Fig. 1 is a side view of the present control in section to show interior elements thereof.

Fig. 2 is a cross-sectional view taken on line 2--2 of Fig. 1.

Fig. 3 is a cross-sectional view taken on line 3-3 of Fig. 1; and

Fig. 4 is a cross sectional view with a portion broken away taken on line 44 of Fig. 1.

Referring more particularly to the accompanying drawings, wherein like and corresponding parts. are designated by similar reference characters, numeral 1 is a cylindrical casing of a material which is preferably a nonconductor of electricity such as glass, rubber, synthetic resins or the like and has an annular side wall 2 with a flange 3 laterally extending therefrom and from which extends contiguously an annular wall 4 the interior surface of which is provided with threads 5. Wall 2 has an inwardly extending lateral flange 6.

Wire 7 extends through wall 2 and is connected to a source of electrical current 8 which in turn is connected to a load at one pole thereof while a further wire 10 is connected to a second pole of said load.

A tubular casing 11 of electrical conducting material has shoulder 12 with peripheral threads 13 extending therefrom. Threads 13 are in threaded engagement with threads detachably connecting casings 1 and 11 with shoulder 12 abutting the end of wall 4 for limiting the connection thereto.

Casing 11 further has a spider-shaped laterally extending flange 14 also of a current conducting material from the central portion of which extends a bearing 15 likewise of a current conducting material. Bearing 1S accordingly extends axially of casing 11 and has an end lateral flange 16. The bore 17 of said hearing has a shaft 18 rotatably mounted therethrough which extends within casing 1 and has a drum 19 fixedly mounted there-- on and extending laterally of casing 1.

The present control drum 19 is of an electrical insulating material and has an electrical resistance wire 20 ring wound therearound with end 21 of said wire connected as at 22 to a conducting hub 23 fixedly mounted on shaft 18.

A bath of mercury 24 is positioned between casing 1 and its flange 6 of a depth for tangentially engaging a portion of the wire 19 presented thereto depending upon the position of drum 19. Wire 7 likewise extends within said bath.

A U-shaped arm 25 of a material attracted to mag- 2,907,970 Patented Oct. 6, 1959 nets has legs 26 and 27 which extend longitudinally of casing 11 due to the connection of said arm at its medial portion to a threaded end 28 of shaft 18. A nut 29 engages said threaded end 28 for retaining said arm on said shaft.

A knob 30 of an electrical insulating material has a U-shaped permanent magnet 31 embedded therein with legs 32 and 33 extending to the flat face 34 of said knob which is of a size and configuration for extending across the open free end 35 of casing 11 whereupon magnet legs 32 and 33 can be positioned adjacent legs 26 and 27 of arm 25 whereupon said magnet will attract said arm forming a magnetic coupling therewith for being rotated together upon the turning of said knob.

A pin 36 extends within said knob 30 at the center of face 34 thereof for hearing against a bar extending across end 35 of casing 11 forming a rotatable support for said knob.

In the assembly of the present device, it is only necessary to position the mercury 24 and drum 19 within casing 1 and attach casing 11 to casing 1 by means of threads 4 and 5 thereby extending shaft 18 through said drum. Hub 23 can be previously attached to the drum or wire 21 can be soldered to said hub if desired. Arm 25 is mounted upon shaft 18 by nut 29 and knob 30 is retained in its operable position by the attraction of magnet 31 for arm 25.

Accordingly, with the apparatus connected by wire 10 to casing 11 current will flow from the supply 8 through Wire 7 into the mercury 24 and from there through wire 20 to hub 23, shaft 18, hearing 15, flange 14 to casing 11 and wire 10. By turning knob 30, arm 25, shaft 18, hub 23, and drum 19 will rotate, varying the portion of resistance wire 20 extending within a mercury bath 24 and accordingly the resistance to the flow of the electrical cunrent passing through said wire 20 will vary with the length of said wire extending from bar 24 to the hub 23. That is, the greater length of wire 20 through which the current must pass will increase the amount of resistance, while if the drum 19 is located so that a shorter length of said wire extends between the bath and said hub, then the resistance will be reduced, thus varying the current passing to load 10.

It is to be appreciated that drum 19 can be composed of a solid resistance material or coated with a resistance material such as carbon in lieu of the wires 2%) but will function in a similar manner. To exchange the drum or rotor employed in casing 1, it is only necessary to detach casing 11 from casing 1 by unscrewing the same and substituting the desired element, that is, drum or rotor, within casing 1 and re-assembling the device.

Drum 19 can be keyed upon shaft 13 as can hub 23 or said hub can be connected to or be a part of said drum.

Housing 1 may comprise an evacuated area to facilitate long usage and life of the device without the usual failures in variable resistors and potentiometers.

The present device is capable of considerable modification and such changes thereto as come within the scope of the appended claims are deemed to be parts of my invention, the new and novel utility comprising the circular shape and movement of a circular formed electrical resistance, through a quantity of mercury or liquid electrical conducting substance, to provide a trouble free variable resistance or potentiometer having a very low contact noise factor.

What I claim is:

1. A rotary electrical circuit control comprising a cylindrical casing of electrical insulating material having threads provided in the open end thereof, a tubular casing of conductive material having a threaded periphery inserted within said open end of said cylindrical casing and in threaded engagement therewith, said cylindrical casing having an internal lateral flange, mercury posifor rotation therewith and into said mercury, electrical resistance means connected to said shaft and carried by said drum for controlling electrical current passing therethrough in accordance with its position relative to and in contact with said mercury, a control knob closing the free end of said tubular casing and connected to said i shaft for rotating same and a pair of wires connected to an electrical circuit with one extending through said cylindrical casing into said mercury and the other connected to said tubular casing.

2. A rotary electrical circuit control as claimed in 4. A rotary electrical circuit control as claimed in claim 1, wherein a U-shaped arm of magnetic attractive material is fixedly connected to said shaft and a permanent magnet is carried by said knob providing a magnetic clutch with said arm for rotation together and holding said knob against one end of said tubular casing closing the same. I V V 5. A rotary electrical circuit control as claimed in claim 1, wherein said tubular easing has an internal laterally extending flange of conductive material supporting said bearing axially of said tubular casing.

6. A rotary electrical circuit as claimed in claim 1 in which said casing is evacuated of air and gases.

References Cited in the file of this patent UNITED STATES PATENTS France Nov. 15, 1951 

